This invention relates to the purification of contaminated water, in particular treatment of groundwater and/or wastewater discharged from industrial and commercial facilities, using iron particles.
A common method for cleaning contaminated groundwater is to build in-ground barriers or curtains with reactive or adsorptive materials. Contaminants are removed when the contaminated water passes through the reactive or adsorptive materials by various physical, chemical and/or biological mechanisms. Such treatment curtains are often called “permeable reactive barriers” (PRBs) as they are usually more water permeable than the native soil/sediment materials. The barriers are semi-permanent or replaceable units that are installed across the flow path of groundwater.
The treatment walls (curtains or barriers) are often installed along with other components, which divert the flow of groundwater through the treatment walls. For example, low permeability cutoff walls can be built adjacent to the treatment walls. The cutoff walls are much less permeable to water so that contaminated water is “funneled” into the treatment wall. This is normally termed the “funnel-and-gate” system in which the funnel is the low permeability wall(s) and the gate is the reactive barrier.
The foremost advantage of the above method is that the contaminated water can be treated in-situ without the need for it to be pumped out for external treatment and disposal. One major disadvantage of the method is the high cost of building the in-ground curtain because of the large amount of soil and sediments that must be dug out and disposed of to accommodate the reactive or adsorptive materials. The cost is especially high for deep aquifers.
Common adsorptive materials include activated carbon and various carbon-based materials. Microorganisms attached to solid materials have also been used in the reactive barriers for treatment of various contaminants such as petroleum hydrocarbons.
Many reactive materials have been suggested. A very fascinating reactive material is metallic iron in the form of iron fillings or powders. The use of iron (metallic or zero-valent iron) for the purification of groundwater impacted by various contaminants has received much research attention over the past decade. It has been shown that iron can react with a wide variety of naturally occurring and man-made contaminants. For example, iron is effective for the transformation of ubiquitous organic solvents such as carbon tetrachloride (CCl4), chloroform (CHCl3), trichloroethene (C2HCl3), and tetrachloroethene (C2Cl4). For example trichloroethene can be reduced according to the following reaction:C2HCl3+4FeO0+5H+→C2H6+4Fe2++3Cl−
Another technique for treating contaminated groundwater in its native place (in situ) involves the direct application of very fine iron powders. The fine iron particles have sizes typically smaller than 100 nanometers, which is at least 10 times smaller than a typical bacterial cell or one thousand times thinner than human hair. These tiny particles are now commonly called nanoparticles. Due to their small sizes, nanoparticles sink slowly and could remain in suspension for extended periods of time. Slurries or suspensions of the iron nanoparticles can be made by mixing the nanoparticles with water, and can be introduced into groundwater by pumping or natural flow. This method has been shown to be effective for cleaning contaminated groundwater.